1. Field of the Invention
The present invention relates, in general, to gears and, more specifically, to gears employed in low force and low speed applications.
2. Background Description
Gears are used in a wide variety of applications to transmit motion between two spaced, rotating shafts. In spur gears, two gears respectively mounted on parallel shafts are meshed together with one gear acting as the driving gear and the other gear being the driven gear. The teeth of such spur gears typically have an involute form laid out along an involute curve. The use of such involute teeth on gears provides smooth rolling action with minimal sliding between the two meshing gears.
In certain gear applications, the center distance between the two rotating, parallel shafts interconnected by two meshed gears is critical for the efficient transfer of rotation between the shafts. If the center distance is too small, the meshing gear teeth may bind or, at least, generate high friction forces which inhibit the smooth rotation of the gears. Conversely, if the center distance between the two shafts is too large, backlash between the gear teeth of the two meshing gears increases which results in looseness between the gears and non-uniform, jerky action of the gears.
In automotive applications, a multi-function steering column switch apparatus is mounted on the vehicle steering column for controlling various electrical devices in the vehicle depending on the mode or direction of movement of the switch. Such devices include, for example, headlight beams, windshield wiper assembly and turn signals. Such devices are separately activated by pivoting, tilting or rotational movement of the multi-function steering column switch lever. Contacts mounted in the switch housing are connected by a specific movement of the lever to control the activation and deactivation of the connected device.
In such applications, rotation of the end portion of the switch lever is typically used to control the windshield wiper assembly between off, on and a plurality of discrete, intermittent operating speeds. A drive gear mounted on and rotatable with the switch lever engages the involute teeth of a spur gear mounted in the switch housing. The spur gear moves a contact attached thereto between engagement with various fixed contacts mounted in the switch housing to selectively control the operation of the windshield wiper assembly depending upon the degree and direction of rotation of the end portion of the switch lever.
For weight and cost reduction purposes, such a gear pair has been made of plastic. However, the tolerances of plastic gears cannot be held as tight as with similar gears formed of metal, especially in gear stacks. This has resulted in high friction forces and non-smooth operation of the switch lever. This also creates an unfavorable tactile feel to the movement of the switch lever.
Thus, it would be desirable to provide a gear arrangement which overcomes the aforementioned problems with respect to providing smooth gear operation within a wide range of gear shaft center tolerances. It would also be desirable to provide such a gear arrangement which is advantageously useful in automotive applications having low force and low speed requirements. It would also be desirable to provide a gear arrangement which provides a solid, uniform tactile feel to a gear operator lever during operation of the gears.